The present invention relates to ethylene/xcex1-olefin copolymers and films obtained from the copolymers. More particularly, the invention relates to ethylene/xcex1-olefin copolymers having excellent moldability, transparency and mechanical strength and also relates to films obtained from the copolymers.
Ethylene copolymers such as ethylene/xcex1-olefin copolymers have been molded by various molding methods, and they have been employed in various fields. The ethylene copolymers are generally prepared by the use of Ziegler catalysts.
In general, the ethylene polymers obtained by the use of titanium catalysts among the Ziegler catalysts have excellent moldability because of their wide molecular weight distribution and wide composition distribution, but their molded products such as films have a problem of surface tackiness.
Meanwhile, it is known that the ethylene polymers obtained by the use of metallocene catalysts among the Ziegler catalysts generally have narrow composition distribution and their molded products such as films have an advantage of low surface tackiness. However, because of narrow molecular weight distribution, these polymers are inferior in the moldability to the ethylene polymers obtained by the use of the titanium catalysts. In the prior art, therefore, the ethylene polymers obtained by one use of the metallocene catalysts have been blended with other polymers to improve the moldability.
Under such circumstances as mentioned above, the present inventors have earnestly studied. As a result, they have found that an ethylene/xcex1-olefin copolymer having the following properties shows excellent moldability though this copolymer is obtained by the use of a metallocene catalyst, and also found that this copolymer has excellent film properties. That is, the ethylene/xcex1-olefin copolymer has the properties: the density and the melt flow rate are each in the specific range; the melt tension and the melt flow rate satisfy the specific relation; the flow index and the melt flow rate satisfy the specific relation; the quantity fraction of a decane-soluble component of the copolymer and the density satisfy the specific relation; the temperature at the position of the maximum peak of an endotherm curve of the copolymer measured by a differential scanning a calorimeter and the density satisfy the specific relation; the endotherm curve of the copolymer measured by a differential scanning calorimeter has two or more melting point peaks, and the temperature at the position of the peak on the lowest temperature side, the temperature at the position of the maximum peak and the density satisfy the specific relation; and a component which is eluted at a temperature or not lower than 100xc2x0 C. in a temperature rise elution test (TREF) exists in the copolymer, and the amount of the eluted component is in the specific range. Based on the finding, the present invention has been accomplished.
It is an object of the present invention to provide an ethylene/xcex1-olefin copolymer showing excellent moldability and capable of producing molded products of excellent transparency and mechanical strength and to provide a film obtained from the copolymer.
The ethylene/xcex1-olefin copolymer according to the invention is a copolymer of ethylene and an xcex1-olefin of 3 to 20 carbon atoms and has the following properties;
(i) the density is in the range of 0.850 to 0.960 g/cm3,
(ii) the melt flow rate at 190xc2x0 C. under a load of 2.16 kg is in the range of 0.1 to 100 g/10 min,
(iii) the melt tension (MT (g)) at 190xc2x0 C. and the melt flow rate (MFR (g/10 min)) satisfy the relation
MTxe2x89xa62.2xc3x97MFRxe2x88x920.84
(iv) the quantity fraction (W (% by weight)) of a decane-soluble component of said copolymer at 23xc2x0 C. and the density (d (g/cm3)) satisfy the relation
in the case of MFRxe2x89xa610 g/10 min:
W less than 80xc3x97exp(xe2x88x92100(dxe2x88x920.88))+0.1,
in the case of MFR greater than 10 g/10 min:
W less than 80xc3x97(MFRxe2x88x929)0.26xc3x97exp(xe2x88x92100(dxe2x88x920.88))+0.1,
(v) the temperature (Tm (xc2x0 C.)) at the position of the maximum peak of an endotherm curve of said copolymer measured by a differential scanning calorimeter and the density (d (g/cm3)) satisfy the relation
Tm less than 400xc3x97dxe2x88x92248,
(vi) the endotherm curve of said copolymer measured by a differential scanning calorimeter has two or more peaks, and the temperature (Tm1 (xc2x0 C.)) at the position of the peak on the lowest temperature side, the temperature (Tm (xc2x0 C.)) at the position of the max mum peak and the density (d (g/cm3)) satisfy the relation
576xe2x88x92600d greater than (Tmxe2x88x92Tm1) greater than 558xe2x88x92600d,
and
(vii) a component, which is eluted at a temperature of not lower than 100xc2x0 C. in a temperature rising elution fractionation test (TREF), exists in said copolymer, and the amount of the eluted component is not more than 10% of the total amount of the eluate.
When the ethylene/xcex1-olefin copolymer is cast molded into a film, the resulting film generally has the following properties:
the film impact strength: (FIS (J/m)) and the density (d (g/cm3)) satisfy the relation
log(FIS) greater than (xe2x88x9250.17xc3x97d)xe2x88x9247.55.
The ethylene/xcex1-olefin copolymer of the invention has excellent moldability, and from the copolymer, molded products having excellent transparency and mechanical strength can be obtained.
The film according to the invention is obtained from the above-described ethylene/xcex1-olefin copolymer.
The cast film according to the invention is obtained by cast molding the ethylene/xcex1-olefin copolymer and has the following properties:
the film impact strength (FIS (J/m)) and the density (d (g/cm3)) satisfy the relation
log(FIS) greater than (xe2x88x9250.17xc3x97d)+47.55.
The film of the invention is excellent not only in mechanical strength, such as impact strength, tear strength and elastic modulus, but also in transparency.